During the monsoons, one often finds a frothy white substance on plants. Many people (including I initially) at first sight believe this to be frog-spawn (foamy bunches of eggs laid by frogs). It is also commonly called "cuckoo spit", "frog spit", "snake spit" etc. owing to its appearance.
These are in fact "houses" made by the nymph (juvenile) of the Froghopper, a type of bug (family Cercopidae). The nymph, commonly called a "spittlebug" is rarely seen outside its house (unless of course the froth is separated). After hatching, it finds a suitable part of the plant, and starts building the house using an interesting method. Plant sap is sucked in and rapidly expelled through the anus, and simultaneously air is forced into the sap through the spiracles (breathing pores on the insect's body). This forms a dense frothy mass, called the spittle. The nymph stays inside the spittle house, feeding on plant sap using its piercing-and-sucking mouth parts.
The spittle house has three major functions-
- It hides the nymph from sight
- It protects the nymph from attacking predators, as the froth is said to have an acrid taste
- It maintains optimum temperature and moisture conditions for the nymph's growth
Most froghopper nymphs I have seen are approx. 3-8mm long. There are several froghopper species, and each had a differently coloured nymph. The most common ones I have seen in the forests around Mumbai are off-white to pale green in colour and approx. 3mm long (probably Cosmoscarta sp.). The red one (pictured below) was found in Matheran, and guessing the length, it was about 8mm long (not sure about the species, I am trying to get it identified and will update this thread accordingly).
(The nymph was not disturbed in any way for the photograph; I found it as it is visible here with the posterior end sticking out of the spittle nest)
(Info courtesy- Indian Insects and Arachnids : A Concise Field Guide by Meenakshi Venkataraman)